1. Field of the Invention
This invention relates to a semiconductor device and a method of manufacturing it, and more particularly to a semiconductor device in which a plurality of semiconductor chips are mounted a planar or superposed manner and a method of manufacturing it.
2. Description of the Related Art
In recent years, in order to increase the capacity of a memory and also extend the circuit function, a plurality of chips are mounted in a single package.
For example, as shown in FIG. 12, a semiconductor device 3 with two semiconductor chips 1 and 2 arranged two-dimensionally is mounted in a single package. The semiconductor device 3 is formed in a lead frame in which a large number of leads 6 are arranged around a first die pad 4 and a second die pad 5. Bridges 7 are arranged between the first die pad 4 and the second die pad 5. The first semiconductor chip 1 is fixed onto the first die pad 4, whereas the second semiconductor chip 2 is fixed onto the second die pad 5. The first bonding pads 8 and 8a on the first and second chips 1 and 2 and the second bonding pads 9 on the leads 6 are connected to each other by metallic wires 10, respectively. The first semiconductor chip 1 and the second semiconductor chip 2 are electrically connected to each other by the bridges 7. The bonding pads 8 of the first semiconductor chip 1 and the bridges 7 are connected to each other by the metallic wires, respectively. Likewise the bridges 7 and the bonding pad 8a on the second semiconductor chip 2 are connected to each other by the metallic wires 10. The entire semiconductor device is mounted in a single package by insulating resin.
Each metallic wire 10 is connected so that its one end is subjected to ball bonding whereas its other end is subjected to stitch bonding. Since the stitch bonding during which ultrasonic wave is applied for a long time deteriorates the semiconductor chip, the ball bonding is adopted on the side of the semiconductor chip, whereas the stitch bonding is adopted on the side of the bonding pad on the lead 6.
However, where the first semiconductor chip 1 and the second semiconductor chip 2 are directly connected to each other by the metallic wires 10, either one of them must be necessarily connected by the stitch bonding. In order to obviate such an inconvenience, in this configuration, the bridges 7 are used to connect both semiconductor chips by the ball bonding.
However, with respect to the lead frame as shown in FIG. 12, the leads 6, which are coupled via a tie bar, can be easily handled. However, the bridges 7, each of which is formed in an island shape, will drop when it stands now. In order to prevent this, various schemes are proposed.
Now, a coupling piece 12 is formed for coupling the first die pad 4 and second die pad 5 with each other. The coupling piece 12 and the bridges 7 are bonded to each other by an adhesive tape.
However, the adhesive tape 13, to which heat is applied during molding, is required to have heat resistance and hence expensive. This leads to cost up of the semiconductor device.
Another technique for supporting the bridges 7 so that they will not drop is to form a lead pattern inclusive of the bridges 7 on a supporting board such as a flexible sheet, a ceramic board and a printed board and mold it. However, adoption of the supporting board increases the thickness of the semiconductor device, and so leads to cost up thereof. Further, the semiconductor chip molded on the supporting board is thermally insulated by the supporting board. This leads to temperature rise of the semiconductor chip. The temperature rise of the semiconductor chip gives rise to reduction of the driving current and driving frequency. This makes it impossible to bring out the inherent capability of the semiconductor chip.